Two-dimensional Photonic Crystal Lasers Research Articles

Far- and near-field investigations on the lasing modes in two-dimensional photonic crystal slab lasers

We present experimental investigations on the lasing modes in two-dimensional (2-D) hexagonal cavities defined by photonic crystals on slab waveguide structures. The far-field emission patterns and near-field intensity distributions of the lasing modes are analyzed in polarization-resolved 2-D angular distribution measurements and spectrally resolved near-field scanning optical microscopy. The far- and near-field analyses result in identification of the various lasing modes and their subsequent classification into one- and two-dimensional modes. In the one-dimensional modes oscillating between two parallel boundaries of the cavities, longitudinal and transverse modes are identified and found to have transverse-electric polarization. In the two-dimensional modes oscillating two-dimensionally in the cavities, various modes including whispering-gallery-like modes are observed and found to exhibit various polarization states.

Two-dimensional photonic crystal semiconductor lasers: computational design, fabrication, and characterization

We have designed, fabricated, and tested two-dimensional (2-D) slab photonic crystal semiconductor lasers at communication wavelengths. Wavelength-size microresonators defined on the 2-D slab photonic crystal have been effective in photon confinement and functioned well as ultra-small lasers by optical pumping. The photonic crystal laser structures that we have tested have shown large quality factors and low thresholds.

Multidirectionally distributed feedback photonic crystal lasers

The lasing mode of a two-dimensional (2D) photonic crystal laser with in-plane multidirectionally distributed feedback effect is analyzed theoretically and experimentally. From an investigation of the Bragg diffraction conditions at several points in the photonic band diagram where lasing is expected, we identify a particular \ensuremath{\Gamma} point at which lasing occurs due to the coupling of lightwaves propagating in six equivalent \ensuremath{\Gamma}-X directions and diffraction normal to the substrate surface. In order to investigate the lasing mode in detail, the distribution of the electromagnetic field at the band edges at the \ensuremath{\Gamma} point is calculated, and each band edge is found to have a different field pattern. The lasing characteristics of the 2D photonic crystal laser at the lasing wavelength corresponding to the \ensuremath{\Gamma} point are measured. Single-mode lasing over a broad circular area is observed by microelectroluminescence measurements under pulsed conditions at room temperature. We also demonstrate the correspondence between the measured lasing wavelengths and calculated band edges by comparing the polarization characteristics with the calculated distribution of the electromagnetic field. The results indicate that 2D coherent lasing oscillation does, in fact, occur due to the multidirectional coupling effect in the 2D photonic crystal. From the theoretical calculation, we show that the polarization patterns of the lasers can be controlled by introducing artificial lattice defects.

Room-temperature operation of VCSEL-pumped photonic crystal lasers

Room-temperature operation of two-dimensional photonic crystal lasers optically pumped by a vertical-cavity surface-emitting laser emitting at 860 nm is reported. The photonic crystal membrane is surrounded by air on both sides and consists of four compressively strained quantum wells as the active region. The incident threshold pump power of an approximately 2.6-μm-diameter hexagonal defect cavity laser operating at 1.6 μm is 2.4 mW.

Recurrent-photon feedback in two-dimensional photonic-crystal lasers

Theoretical studies are carried out for the close-to-lasing two-dimensional finite-size photonic crystals. On the basis of the simulations on the field-intensity distributions and the photon-energy flux distributions, this paper demonstrates the occurrence of a different type of positive feedback of light, which can be called recurrent-photon feedback. This feedback mechanism can be construed as an extension of the feedback mechanism in ordinary one-dimensional distributed-feedback lasers.

Polarization mode control of two-dimensional photonic crystal laser by unit cell structure design.

We demonstrate polarization mode selection in a two-dimensional (2D) photonic crystal laser by controlling the geometry of the unit cell structure. As the band diagram of the square-lattice photonic crystal is influenced by the unit cell structure, calculations reveal that changing the structure from a circular to an elliptical geometry should result in a strong modification of the electromagnetic field distributions at the band edges. Such a structural modification is expected to provide a mechanism for controlling the polarization modes of the emitted light. A square-lattice photonic crystal with the elliptical unit cell structure has been fabricated and integrated with a gain media. The observed coherent 2D lasing action with a single wavelength and controlled polarization is in good agreement with the predicted behavior.

Two-dimensional photonic crystal laser mirrors

Ridge waveguide lasers with an integrated 2D photonic crystal (PC)mirror have been successfully fabricated on anInGaAs/AlGaAs laser structure emitting around 995 nm. Theinvestigated 2D PCs consist of air holes in a semiconductorarranged in a triangular lattice with periods from a = 180 to400 nm with different lattice orientations. This is fabricatedusing high-resolution 100 kV electron beam lithography inconnection with a triple-metal-layer mask and electroncyclotron resonance dry etching, yielding etch depths around550 nm. The capability of this fabrication technology forsemiconductor feature sizes down to 30 nm is demonstrated.The performance of the lasers with a PC mirror with respect toboth laser threshold and differential efficiency clearlydepends on the period and orientation of the PC lattice. Thisbehaviour can be understood using simulations of the PCreflectivity based on 2D transfer matrix methods andfinite-element analysis of the waveguide properties. Thefeedback from the PC mirror is confirmed using Fouriertransform reflectometry analysis of a sub-threshold laserspectrum.

Directional lasing oscillation of two-dimensional organic photonic crystal lasers at several photonic band gaps

We fabricated a series of two-dimensional (2D) hexagonal organic photonic-crystal lasers whose lattice constant varies from 0.18 to 0.44 μm, and observed clear lasing oscillation at the four lowest band gap frequencies (M1, K2, M2, and Γ1). We used in-plane beam propagation analysis to clarify the 2D feedback mechanism at each gap frequency, which differs for different gaps. The observed K1 lasing oscillation is due to coupling of three nonparallel diffracted waves, which has a purely 2D character. This shows that photonic crystal lasers can operate with various feedback essentially different from that of conventional 1D distributed feedback lasers.

Threshold gain and gain-enhancement due to distributed-feedback in two-dimensional photonic-crystal lasers

The threshold gain (gth) of a two-dimensional (2D) photonic crystal distributed-feedback (DFB) laser composed of 8×8 dielectric cylinders was one order of magnitude smaller than that of an 8-pair 1D DFB laser with the identical refractive indexes. In the 2D finite-width photonic crystal laser, gth using the 1st photonic band was smaller than that using the higher photonic band, contrary to the expectation from the flatness of the photonic band structures. This unexpected gth is probably due to the longer optical path caused by the reflection at the side boundary. Moreover, gth using the 1st photonic band was the smallest in the Γ–X direction of the square-lattice photonic crystal. The gain-enhancement using the 1st–3rd photonic bands were 10–30 in the 2D photonic crystal and that using the 3rd band was the largest. The gain-enhancement using the 1st photonic band of the 2D photonic crystal consisting of dielectric cylinders was larger than that of air cylinders.

Continuous room-temperature operation of optically pumped two-dimensional photonic crystal lasers at 1.6 μm

Summary form only given. The complete presentation was not made available for publication as part of the conference proceedings.

Lithographic tuning of a two-dimensional photonic crystal laser array

One attraction of photonic crystals is the ability to control optical device characteristics by lithographically varying the geometry. In this letter, we demonstrate a 10/spl times/10 array of optically pumped two-dimensional (2-D) photonic crystal defect lasers with varying lattice parameters. By adjusting the photonic crystal interhole spacing as well as the hole diameter we are able to tune the laser wavelength from 1500 to 1625 nm on a monolithic InP-InGaAsP wafer. A wavelength resolution of 10 nm from device to device was obtainable, limited by the lithography and etching tolerances of our fabrication method.

Emission characteristics of two-dimensional organic photonic crystal lasers fabricated by replica molding

We report on the far-field emission characteristics of two-dimensional photonic crystal-based organic waveguide lasers. The photonic crystals possess square vein, triangular, and honeycomb symmetries. The two-dimensional gratings are fabricated by employing soft lithographic methods. The far-field pattern that we observe is a result of out-of-plane diffractive coupling of the laser emission generated in the plane of the waveguide. This emission pattern offers a convenient and powerful way to evaluate the nature of laser action in such resonators. In devices which possess defects/breaks in the periodicity of the two-dimensional grating, laser emission generated in-plane is scattered in the plane of the waveguide. This phenomenon is the photonic crystal analogue of Kikuchi scattering in electronic crystals.

Lasing mechanism in two-dimensional photonic crystal lasers

We conduct a comprehensive investigation of the lasing mechanism in a photonic crystal slab laser with a refractive index that is periodic in two dimensions. Experimental spectra of laser structures fabricated with organic gain media are presented. It is found that lasing frequencies can be explained in terms of Van Hove singularities in the density of modes. We also observe lasing spectra that cannot be obtained from structures with one-dimensional periodicity, such as traditional distributed feedback lasers. Lasing frequencies are computed using numerical techniques.